Kasper Dideriksen

Stimulation of muscle protein synthesis by whey and caseinate ingestion after resistance exercise in elderly individuals

Sarcopenia is a well‐known phenomenon in elderly individuals and resistance exercise together with sufficient amino acid (AA) availability has proved to be a counteractive implement. However, the source of AA and supplement timing require further investigation. The objective was to compare muscle protein synthesis (MPS) to intakes of whey and caseinate after heavy resistance exercise in healthy elderly individuals, and, furthermore, to compare the timing effect of caseinate intake. Twenty‐four elderly men and women (mean ± SEM; 68 ± 1 years) were randomized to one of four groups: caseinate intake before exercise (CasPre), caseinate intake immediately after exercise (CasPost), whey intake immediately after exercise (Whey), or intake of a non‐caloric control drink (Control). Muscle myofibrillar and collagen fractional synthesis rates (FSR) were measured by a primed continuous infusion of l‐[1‐13C]leucine using labeled proteins during a 6‐h recovery period. No differences were observed in muscle myofibrillar and collagen FSR with Whey (0.09 ± 0.01%/h) compared with CasPost (0.09 ± 0.003%/h), and it did not differ between CasPre (0.10 ± 0.01%/h) and CasPost. MPS does not differ with whey and caseinate feeding immediately after heavy resistance exercise in elderly individuals, and MPS is similar with caseinate ingestion before and after exercise.

Influence of Amino Acids, Dietary Protein, and Physical Activity on Muscle Mass Development in Humans

Ingestion of protein is crucial for maintenance of a variety of body functions and within the scope of this review we will specifically focus on the regulation of skeletal muscle mass. A quantitative limitation exists as to how much muscle protein the body can synthesize in response to protein intake. Ingestion of excess protein exerts an unwanted load to the body and therefore, it is important to find the least amount of protein that provides the maximal hypertrophic stimulus. Hence, research has focused on revealing the relationship between protein intake (dose) and its resulting stimulation of muscle protein synthesis (response). In addition to the protein amount, the protein digestibility and, hence, the availability of its constituent amino acids is decisive for the response. In this regard, recent studies have provided in-depth knowledge about the time-course of the muscle protein synthetic response dependent on the characteristics of the protein ingested. The effect of protein intake on muscle protein accretion can further be stimulated by prior exercise training. In the ageing population, physical training may counteract the development of “anabolic resistance” and restore the beneficial effect of protein feeding. Presently, our knowledge is based on measures obtained in standardized experimental settings or during long-term intervention periods. However, to improve coherence between these types of data and to further improve our knowledge of the effects of protein ingestion, other investigative approaches than those presently used are requested.

Activated Protein Synthesis and Suppressed Protein Breakdown Signaling in Skeletal Muscle of Critically Ill Patients

Background Skeletal muscle mass is controlled by myostatin and Akt-dependent signaling on mammalian target of rapamycin (mTOR), glycogen synthase kinase 3β (GSK3β) and forkhead box O (FoxO) pathways, but it is unknown how these pathways are regulated in critically ill human muscle. To describe factors involved in muscle mass regulation, we investigated the phosphorylation and expression of key factors in these protein synthesis and breakdown signaling pathways in thigh skeletal muscle of critically ill intensive care unit (ICU) patients compared with healthy controls. Methodology/Principal Findings ICU patients were systemically inflamed, moderately hyperglycemic, received insulin therapy, and showed a tendency to lower plasma branched chain amino acids compared with controls. Using Western blotting we measured Akt, GSK3β, mTOR, ribosomal protein S6 kinase (S6k), eukaryotic translation initiation factor 4E binding protein 1 (4E-BP1), and muscle ring finger protein 1 (MuRF1); and by RT-PCR we determined mRNA expression of, among others, insulin-like growth factor 1 (IGF-1), FoxO 1, 3 and 4, atrogin1, MuRF1, interleukin-6 (IL-6), tumor necrosis factor α (TNF-α) and myostatin. Unexpectedly, in critically ill ICU patients Akt-mTOR-S6k signaling was substantially higher compared with controls. FoxO1 mRNA was higher in patients, whereas FoxO3, atrogin1 and myostatin mRNAs and MuRF1 protein were lower compared with controls. A moderate correlation (r2 = 0.36, p<0.05) between insulin infusion dose and phosphorylated Akt was demonstrated. Conclusions/Significance We present for the first time muscle protein turnover signaling in critically ill ICU patients, and we show signaling pathway activity towards a stimulation of muscle protein synthesis and a somewhat inhibited proteolysis.

Tendon and skeletal muscle matrix gene expression and functional responses to immobilisation and rehabilitation in young males: effect of growth hormone administration

•  Loss of muscle and tendon function during periods of immobilisation and rehabilitation represents a challenge in clinical medicine. •  It is not known to what extent growth hormone (GH) supplementation is able to counteract the absence of mechanical loading during immobilisation in musculo‐tendinous connective tissue. •  This study examines the effect of GH in musculo‐tendinous connective tissue in humans during immobilisation and subsequent rehabilitation. •  The main study findings were the observation that GH supplementation stimulates collagen expression in musculo‐tendinous tissue and abolishes the normal decline in tendon stiffness and lysyl oxidase during immobilisation. Furthermore, GH supplementation results in an increased tendon size and stiffness during rehabilitation. •  GH supplementation has a matrix‐stabilising effect during periods of inactivity and rehabilitation in humans.

Effect of growth hormone on aging connective tissue in muscle and tendon: gene expression, morphology, and function following immobilization and rehabilitation

It is unknown whether loss in musculotendinous tissue during inactivity can be counteracted by growth hormone (GH), and whether GH accelerate rehabilitation in aging individuals. Elderly men (65-75 yr; n = 12) had one leg immobilized 2 wk followed by 6 wk of retraining and were randomly assigned to daily injections of recombinant GH (rhGH; n = 6) or placebo (Plc; n = 6). Cross-sectional area (CSA), muscle strength (MVC), and biomechanical properties of m. quadriceps and patellar tendon were determined. Muscle and tendon biopsies were analyzed for gene expressions (mRNA) of collagen (COL1A1/3A1) and insulin-like growth factors (IGF-1Ea/Ec). Fibril morphology was analyzed by transmission electron microscope (TEM). In tendon, CSA and biomechanical properties did not change following immobilization, but an increase in CSA was found after 6 wk of rehabilitation in both groups. The changes were more pronounced when GH was injected. Furthermore, tendon stiffness increased in the GH group. Muscle CSA declined after immobilization in the Plc but not in the GH group. Muscle CSA increased during retraining, with a significantly larger increase in the GH group compared with the Plc group. Both a time and a group effect were seen for IGF-1Ea/Ec and COL1A1/3A1 mRNA expression in muscle, with a difference between GH and Plc. IGF-1Ea/Ec and COL-1A1/3A1 mRNA expression increased in muscle following immobilization and retraining in subjects receiving GH, whereas an increase in IGF-1Ec mRNA expression was seen in the Plc group only after retraining. In conclusion, in elderly humans, GH seems to have a matrix stabilizing effect during inactivity and rehabilitation by stimulating collagen expression in the musculotendinous tissue and increasing tendon CSA and stiffness.

Effect of acute exercise on patella tendon protein synthesis and gene expression

Evidence suggests that habitual loading can result in patellar tendon hypertrophy, especially at the proximal and distal parts of the patellar tendon. The underlying protein kinetic changes and its regulation remains controversial and human data, investigating this topic, are limited. The present study investigated how acute exercise affects growth factor production and collagen fractional synthetic rate in patellar tendon tissue from patients undergoing an anterior cruciate ligament reconstruction operation. The operation was performed by use of the bone-patellar tendon-bone method under spinal anesthesia.Twelve subjects were randomized to one of two groups: a control group or an exercise group (1-hr unilateral knee-extension 67% of Wmax 24 hours before operation). Two hours before the anterior cruciate ligament operation a flooding-dose of L-[1-13C]proline was given. Tissue from the most proximal part of the patellar tendon was obtained during the operation. Tendon collagen fractional synthetic rate and mRNA concentrations of TGF-β-1, CTGF, and type I and III collagen were measured.CTGF and type I collagen expression were higher in the exercise group compared to the control group (p < 0.05). Type III collagen expression (p = 0.11), TGF-β-1 expression (p = 0.34), and collagen fractional synthetic rate (p = 0.26) did not differ between groups.Although the expression of CTGF and type I collagen were higher, the patellar tendon collagen fractional synthetic rate was not correspondingly higher after exercise. The elevated CTGF expression in the exercise group indicates that the TGF-beta pathway could be an important link between mechanical loading and stimulation of tendon tissue type I collagen expression.

The single-biopsy approach in determining protein synthesis in human slow-turning-over tissue: use of flood-primed, continuous infusion of amino acid tracers.

Muscle protein synthesis (MPS) rate is determined conventionally by obtaining two or more tissue biopsies during a primed, continuous infusion of a stable isotopically labeled amino acid. The purpose of the present study was to test whether tracer priming given as a flooding dose, thereby securing an instantaneous labeling of the tissue pools of free tracee amino acids, followed by a continuous infusion of the same tracer to maintain tracer isotopic steady state, could be used to determine the MPS rate over a prolonged period of time by obtaining only a single tissue biopsy. We showed that the tracer from the flood prime appeared immediately in the muscle free pool of amino acids and that this abundance could be kept constant by a subsequent continuous infusion of the tracer. When using phenylalanine as tracer, the flood-primed, continuous infusion protocol does not stimulate the MPS rate per se. In conclusion, the flood-primed, continuous infusion protocol using phenylalanine as tracer can validly be used to measure the protein synthesis rate in human in vivo experiments by obtaining only a single tissue biopsy after a prolonged infusion period.

Skeletal muscle adaptation to immobilization and subsequent retraining in elderly men: No effect of anti-inflammatory medication

BACKGROUND Non-steroidal anti-inflammatory drugs (NSAIDs) may enhance resistance training induced gain in skeletal muscle mass and strength, but it is unknown if NSAIDs affects muscle loss during periods of inactivity in elderly individuals. Thus, we studied the influence of NSAID treatment on human skeletal muscle during immobilization and rehabilitation resistance training (retraining). METHODS 19 men (60-80yrs, range) were randomly assigned to ibuprofen (1200mg/d, Ibu) or placebo (Plc). One lower limb was immobilized in a cast for 2weeks and retrained for 6weeks. Moreover, whey protein isolate was ingested (2×20g/d) throughout the whole study period. Plasma inflammatory markers, quadriceps muscle mass and strength, and muscle gene expression were investigated. RESULTS Muscle mass and strength decreased after 2weeks of immobilization (P<0.001), but returned to baseline levels after 2weeks of retraining combined with whey protein supplementation (P<0.001). Furthermore, muscle mass and strength reached beyond baseline levels after 6weeks of retraining (p<0.05), and NSAID did not significantly affect this (p>0.05). No group-differences, but differences over time, were observed for muscle gene expression of proteolytic and anabolic factors. Plasma inflammatory markers were unaffected by the study intervention and NSAID treatment. CONCLUSION Two weeks of lower limb immobilization lead to a reduction in muscle mass and strength, but these parameters were restored already after2 weeks of retraining and whey protein supplementation. After 6weeks of retraining and whey protein supplementation, muscle mass and strength increased beyond baseline levels, and NSAID treatment did not significantly influence this in elderly.

No effect of anti-inflammatory medication on postprandial and postexercise muscle protein synthesis in elderly men with slightly elevated systemic inflammation.

BACKGROUND Based on circulating C-reactive protein (CRP) levels, some individuals develop slightly increased inflammation as they age. In elderly inflamed rats, the muscle response to protein feeding is impaired, whereas it can be maintained by treatment with non-steroidal anti-inflammatory drugs (NSAIDs). It is unknown whether this applies to elderly humans with increased inflammation. Thus, the muscle response to whey protein bolus ingestion with and without acute resistance exercise was compared between healthy elderly individuals and elderly individuals with slightly increased inflammation±NSAID treatment. METHODS Twenty-four elderly men (>60years) were recruited. Of those, 14 displayed a slightly increased systemic inflammation (CRP>2mg/l) and were randomly assigned to NSAID (Ibuprofen 1800mg/day) or placebo treatment for 1week. The remaining 10 elderly individuals served as healthy controls (CRP<1mg/l). The muscle protein synthetic response was measured as the fractional synthetic rate (FSR) and p70S6K phosphorylation-to-total protein ratio. RESULTS The basal myofibrillar FSR and the myofibrillar FSR responses to whey protein bolus ingestion with and without acute resistance exercise were maintained in inflamed elderly compared to healthy controls (p>0.05) and so was p70S6K phosphorylation. Moreover, NSAID treatment did not significantly improve the myofibrillar and connective tissue FSR responses or reduce the plasma CRP level in inflamed, elderly individuals (p>0.05). CONCLUSION A slight increase in systemic inflammation does not affect the basal myofibrillar FSR or the myofibrillar FSR responses, which suggests that elderly individuals with slightly increased inflammation can benefit from protein ingestion and resistance exercise to stimulate muscle protein anabolism. Moreover, the NSAID treatment did not significantly affect the myofibrillar or connective tissue FSR responses to protein ingestion and acute resistance exercise.

Tendon collagen synthesis declines with immobilization in elderly humans: no effect of anti-inflammatory medication

Nonsteroidal anti-inflammatory drugs (NSAIDs) are used as pain killers during periods of unloading caused by traumatic occurrences or diseases. However, it is unknown how tendon protein turnover and mechanical properties respond to unloading and subsequent reloading in elderly humans, and whether NSAID treatment would affect the tendon adaptations during such periods. Thus we studied human patellar tendon protein synthesis and mechanical properties during immobilization and subsequent rehabilitating resistance training and the influence of NSAIDs upon these parameters. Nineteen men (range 60-80 yr) were randomly assigned to NSAIDs (ibuprofen 1,200 mg/day; Ibu) or placebo (Plc). One lower limb was immobilized in a cast for 2 wk and retrained for 6 wk. Tendon collagen protein synthesis, mechanical properties, size, expression of genes related to collagen turnover and remodeling, and signal intensity (from magnetic resonance imaging) were investigated. Tendon collagen synthesis decreased (P < 0.001), whereas tendon mechanical properties and size were generally unchanged with immobilization, and NSAIDs did not influence this. Matrix metalloproteinase-2 mRNA tended to increase (P < 0.1) after immobilization in both groups, whereas scleraxis mRNA decreased with inactivity in the Plc group only (P < 0.05). In elderly human tendons, collagen protein synthesis decreased after 2 wk of immobilization, whereas tendon stiffness and modulus were only marginally reduced, and NSAIDs had no influence upon this. This indicates an importance of mechanical loading for maintenance of tendon collagen turnover. However, reduced collagen production induced by short-term unloading may only marginally affect tendon mechanical properties in elderly individuals. NEW & NOTEWORTHY In elderly humans, 2 wk of inactivity reduces tendon collagen protein synthesis, while tendon stiffness and modulus are only marginally reduced, and NSAID treatment does not affect this. This indicates that mechanical loading is important for maintenance of tendon collagen turnover and that changes in collagen turnover induced by short-term immobilization may only have minor impact on the internal structures that are essential for mechanical properties in elderly tendons.